Description:

Objective:

The upper Great Lakes region contains a wide forest transition zone where temperate and boreal tree species reach their northern and southern range limits, respectively. Local factors such as resource availability, competition, and browsing by deer affect tree regeneration trends and may facilitate or impede tree species responses to climate change. The objective of this research is to understand how a warming climate in conjunction with varying levels of local factors are influencing the performance of temperate and boreal tree species in the seedling and sapling layers of transition zone forests.

Synopsis

Climate change is forecast to cause major shifts in tree species distributions. In the Great Lakes region, forests dominated by boreal spruce and fir may transition to temperate maple and oak. My research examines initial signs of forest change in the seedling and sapling layers and quantifies the effects of climate on the performance and competitive interactions of temperate and boreal species. These findings will enable land managers to prepare for the rate and direction of forest change.

Approach:

Because trees are long-lived, initial evidence of forest response to climate change should be found in the younger understory regeneration layers. I will compare the performance of temperate and boreal regeneration through field studies of relative abundance patterns, growth rates, and survival. The common tree species in this study are balsam fir (Abies balsamea), white spruce (Picea glauca), sugar maple (Acer saccharum), red maple (Acer ruburm), red oak (Quercus rubra), and American basswood (Tilia americana). Field sites span a 2.5 °C temperature gradient across northern Minnesota, Wisconsin, and Michigan. I will examine how species abundances change with size class from the low seedlings up to the overstory tree layer. Using radial and height growth rates, I will assess how the competitive abilities of each species changes with temperature, browse pressure, and other factors. Finally, I will follow the survival of marked seedlings over several growing seasons to compare survival rates.

Expected Results:

I expect to find individualistic species level responses to interacting ecosystem drivers. In general, temperate species should show a greater positive response to temperature through enhanced growth rates, higher survival, and greater understory abundance levels than boreal species, supporting predictions of temperate species northern expansion. However, because temperate broadleaf saplings are also preferred browse species, areas with heavy browse pressure may favor unpalatable boreal spruce and fir. Overstories dominated by boreal conifers create low light and nutrient poor conditions that will also limit temperate species response to temperature. These findings will indicate whether species specific responses to climate are inhibited or promoted by other factors such as browse pressure and resource availability.

Potential to Further Environmental/Human Health Protection

Understanding forest responses to climate warming is necessary to ensure the economic and ecological health of the region and this research will create empirical knowledge needed to inform land management and policy decisions aimed at mitigating climate change impacts.

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.